The present invention relates to an ion implanter provided with a plurality of plasma source bodies.
The field of the invention is that of ion implanters operating in plasma immersion mode. Thus, implanting ions in a substrate consists in immersing the substrate in a plasma and in biasing it with a negative voltage of a few tens of volts to a few tens of kilovolts (kV) (generally at least 100 kV), in order to create an electric field that is capable of accelerating the ions of the plasma towards the substrate.
The penetration depth of the ions is determined by their acceleration energy. It depends firstly on the voltage applied to the substrate and secondly on the respective natures of the ions and of the substrate. The concentration of implanted atoms depends on the dose, which dose is expressed as a number of ions per square centimeter (cm2), and also on the implantation depth.
The plasma is generated within a source body that is arranged facing the substrate carrier. The source body is in the form of a cylindrical segment that is free from any inside obstacle; it opens out into the enclosure of the implanter. Around each source body, there is a radiofrequency antenna that is provided to generate the plasma. In general, the cylinder constituting the source body is a circular cylinder.
The diameter of the source body is necessarily limited since plasma density decreases with increasing distance from the antenna. In order to conserve a satisfactory plasma density at the center of the source body, this diameter thus generally lies in the range 100 millimeters (mm) to 200 mm.
The plasma extends from the source body towards the substrate carrier with a hyperboloid profile. As a result, a substrate of large size needs to be placed relatively far from the substrate carrier if it is desired for implantation to take place over its entire area.
This spacing has the consequence of significantly reducing the density of the plasma at the level of the substrate. As a result, for a given dose, the time required for implantation is considerably increased.
Thus, Document EP 0 480 688 teaches an arrangement of plasma sources for ion implantation. The implanter has an enclosure in which a substrate carrier is arranged that is connected to a substrate power supply via a high voltage electrical passage, the enclosure being provided with pump means, the enclosure also including a cylindrical source body free from any obstacle and arranged facing the substrate carrier, the enclosure including at least one additional cylindrical source body that is also free from any obstacle and that is also arranged facing the substrate carrier.
Mention may also be made of Document U.S. Pat. No. 6,300,227, which describes an ion implantation system operating by plasma immersion analogous to that described above.
In both of those documents, magnetic confinement means are provided for the enclosure. Unfortunately, such an arrangement is not good for plasma uniformity.